System and method for seawater desalination based on solar energy

Abstract

A system and method for seawater desalination based on solar energy. In the system, the second reaction tank is connected with the first reaction tank via a cation-selective nano-film and includes the same volume and concentration of seawater as the first reaction tank. The pump is connected the second reaction tank with the third reaction tank to pump the seawater solution after the removal of cationic salts from the second tank into the third tank. The fourth reaction tank is connected to the third reaction tank via a anion-selective nano-film. The third and fourth reaction tanks are connected through a second external channel and include the same volume and concentration of seawater, and the second external channel is provided with a third valve to control the flow of liquid. The fourth reaction tank is provided with a liquid output channel.

1 . A system for seawater desalination based on solar energy, comprising:
 a. a first reaction tank, arranged with a first electrode immersed in seawater;   b. a second reaction tank, connected to the first reaction tank via a cation-selective nano-film and arranged with a second electrode immersed in seawater, wherein the first reaction tank and the second reaction tank are connected through an external channel and include the same volume and concentration of seawater, and the external channel is provided with a first valve to control the flow of liquid, and wherein the first electrode and the second electrode are connected through a first external circuit;   c. a pump, connecting the second reaction tank and a third reaction tank to pump the seawater solution after the removal of cationic salts from the second reaction tank into the third reaction tank;   d. the third reaction tank, arranged with a third electrode immersed in the seawater solution; and   e. a fourth reaction tank, connected to the third reaction tank via a anion-selective nano-film and arranged with a fourth electrode immersed in the seawater, wherein the third reaction tank and the fourth reaction tank are connected through a second external channel and include the same volume and concentration of seawater, and the second external channel is provided with a third valve to control the flow of liquid, wherein the third electrode and the fourth electrode are connected through a second external circuit, and wherein the fourth reaction tank is provided with a liquid output channel.   
     
     
         2 . The system for seawater desalination based on solar energy of  claim 1 , wherein the cation-selective nano-film and the anion-selective nano-film comprise parallel pore ion channels from the second reaction tank to the first reaction tank and from the fourth reaction tank to the third reaction tank, respectively. 
     
     
         3 . The system for seawater desalination based on solar energy of  claim 2 , wherein the cation-selective nano-film and/or the anion-selective nano-film is single- or multi-layer porous semiconductor membranes with an average pore size of 2-30 nm, a thickness of each layer of not more than 100 nm, and a total thickness of not more than 500 nm. 
     
     
         4 . The system for seawater desalination based on solar energy of  claim 2 , wherein the parallel pore ion channels of the cation-selective nano-film comprise negatively charged surface layers. 
     
     
         5 . The system for seawater desalination based on solar energy of  claim 2 , wherein the parallel pore ion channels of the anion-selective nano-film comprise a positively charged surface layers. 
     
     
         6 . The system for seawater desalination based on solar energy of  claim 1 , wherein the first reaction tank, the second reaction tank, the third reaction tank and/or the fourth reaction tank are made of quartz glass. 
     
     
         7 . The system for seawater desalination based on solar energy of  claim 1 , wherein the cation-selective nano-film are respectively connected to the first reaction tank and the second reaction tanks via flanges, and the anion-selective nano-film are respectively connected to the third and fourth reaction tanks via flanges. 
     
     
         8 . The system for seawater desalination based on solar energy of  claim 1 , wherein the pump is provided with a second valve, and the liquid output channel is provided with a fourth valve; the first external circuit is provided with a first electric signal collector for controlling system to start or stop, and/or the second external circuit is provided with a second electric signal collector for controlling system to start or stop. 
     
     
         9 . A method for desalination by means of the system for seawater desalination based on solar energy as defined in  claim 1 , comprising the following steps:
 i: irradiating the cation-selective nano-film by sunlight through the second reaction tank, and absorbing solar energy to excite carriers;   ii: generating the difference in electrochemical potential energy to enable the cations of the seawater in the second reaction tank to enter the first reaction tank through an ion channel of cation-selective nano-film;   iii: generating diffusion potential on the two sides of the cation-selective nano-film until the current is stable, and collecting signals to control the system to shield light signals by a first electric signal collector, wherein a cation concentration of the liquid in the second reaction tank is lower than that in the first reaction tank;   iv: opening a second valve and pump to discharge the seawater solution in the second reaction tank to the third reaction tank; and   v: closing the second valve and the pump, followed by opening the first valve to introduce liquid in the first reaction tank into the second reaction tank, then closing the first valve when the volume of liquid in the first reaction tank is equal to that in the second reaction tank, and then returning to the irradiating step for cyclic desalination.   
     
     
         10 . A method for desalination by means of the system for seawater desalination based on solar energy as defined in  claim 1 , comprising the following steps:
 i: opening the third valve to introduce liquid in the third reaction tank into the fourth reaction tank, and then closing the third valve when the volume of liquid in the third reaction tank is equal to that in the fourth reaction tank;   ii: irradiating the anion-selective nano-film by sunlight through the third reaction tank, and absorbing solar energy to excite carriers by the surface of the film;   iii: generating the difference in electrochemical potential energy based on a photo-Dember effect to enable the anion of seawater in the fourth reaction tank to enter the third reaction tank through an anion-selective nano-film ion channel;   iv: generating diffusion potential on the two sides of the anion-selective nano-film until the current is stable, and collecting signals to control system to shield light signals by a second electric signal collector, wherein an anion concentration of liquid in the fourth reaction tank is lower than that in the third reaction tank;   v: opening a fourth valve to discharge the liquid in the fourth reaction tank; and   vi: closing the fourth valve and introducing the liquid in the third reaction tank into the fourth reaction tank, then closing the third valve when the volume of liquid in the fourth reaction tank is equal to that in the third reaction tank, and then returning to the opening step for circular desalination.